1. Field of the Invention
The present invention relates to a method measuring the thicknesses and the refractive indices of component layers of a sample laminated structure, and a measuring apparatus for carrying out the same.
2. Description of the Related Art
A low-coherence interferometry is used for measuring the optical thickness of a transparent sample, such as a thin film or an optical glass. The low-coherence interferometry is carried out by an interferometer using white light or light emitted by a low-coherence light source, such as a light emitting diode. The low-coherence interferometry finds out the absolute position of a sample from the position of a reference mirror by using a fact that interference fringes appear only near a position where the difference between the two optical path lengths is zero. The low-coherence interferometry is applied to the absolute measurement of a block gage, the calibration of a base line and surface protilometry. Recently, active studies on a measuring method developed by extending the low-coherence interferometry have been reported in the fields of ophthalmology and biological science.
A known confocal laser microscope projects a laser beam on a sample in a spot, and forms an image of reflected light reflected by the sample or fluorescent light emitted by the sample on a point detector. The confocal laser microscope, as compared with conventional optical microscopes, is capable of forming an image of a high contrast and of forming a three-dimensional image with a high axial resolution, i.e., resolution along the optical axis. Therefore, the confocal laser microscope is used prevalently for measuring the morphology of a surface and observing biological specimens. The high axial resolution of the confocal laser microscope is effectively applicable to the measurement of optical thicknesses of component layers of a transparent laminated structure.
However, a value directly determined on the basis of the principle of the confocal laser microscope is an optical thickness and hence the refractive index of the corresponding layer must be determined by another method to convert the optical thickness into a corresponding geometrical thickness. Such a problem arises also in thickness measurement by the foregoing low-coherence interferometry. However, there has not been proposed any refractive index measuring method capable of measuring the respective indices of the component layers of a sample laminated structure without destroying the sample laminated structure.